1. Field of the Invention
The present invention relates generally to piezoelectric ceramic compositions that are useful as materials for piezoelectric elements such as piezoelectric ceramic filters, piezoelectric ceramic vibrators, actuators, piezoelectric transformers, various types of sensors, or the like.
2. Related Background Art
Conventionally, as piezoelectric ceramic materials, lead titanate-based ceramics containing PbTiO3 as a main component, lead zirconate titanate-based ceramics containing Pb(Ti, Zr)O3 as a main component, and a multicomponent piezoelectric ceramic that includes some kinds of complex perovskite compositions, for example, Pb(Mg1/3Nb2/3)O3, Pb(Ni1/3Nb2/3)O3 have been used. With these compositions, piezoelectric ceramics having different characteristics in accordance with the intended uses can be obtained through the suitable selection of a composition ratio of the components thereof. These piezoelectric ceramics are used for ceramic filters, piezobuzzers, piezoelectric spark plugs, ultrasonic piezoelectric transducers, or the like.
However, conventional lead zirconate titanate piezoelectric ceramics have a small frequency constant that is about 2000 Hzxc2x7m. Hence, when using such a piezoelectric ceramics, a resonator in which thickness longitudinal vibration occurs in the frequency band of about 10 MHz or higher has an element thickness of 0.2 mm or less, which makes the manufacture thereof difficult. In addition, the above-mentioned conventional materials contain a large amount of lead as a main component, which is not desirable from the viewpoint of environmental protection. The above-mentioned conventional materials have large grain sizes and thus it is difficult to use them for vibrators used at high frequencies. Furthermore, it is desired that piezoelectric ceramics have a high mechanical quality factor Qm (hereinafter referred to as xe2x80x9cmechanical Qxe2x80x9d).
Hence, an object of the present invention is to provide a piezoelectric ceramic composition that is manufactured easily by an ordinary sintering method, is free from lead, and has a large frequency constant, a small grain size, and a high mechanical Q at least in its preferable embodiments. Another object of the present invention is to provide a piezoelectric element including this piezoelectric ceramic composition.
From one aspect of the present invention, a first piezoelectric ceramic composition is expressed by a formula of (1-v-w)[(Li1-x-yNaxKy)zRO3].vLMnO3. wBi1/2Na1/2TiO3.
In the above formula, 0xe2x89xa6vxe2x89xa60.05, 0xe2x89xa6wxe2x89xa60.2, v+w greater than 0, 0.2xe2x89xa6xxe2x89xa60.97, 0xe2x89xa6yxe2x89xa60.8, x+yxe2x89xa70.8, 0.98xe2x89xa6zxe2x89xa61, L indicates at least one element selected from the rare earth elements (Sc, Y, and lanthanide series elements), and R denotes at least one element selected from Nb, Ta, and Sb.
From another aspect of the present invention, a second piezoelectric ceramic composition includes at least one selected from Mn, Cr, and Co that is added to a composition expressed by a formula of (Li1-x-yNaxKy)zRO3 so as to have a ratio thereof to the whole of 0.01 to 1 wt % in terms of MnO2, Cr2O3, and CoO, respectively.
In the formula, x, y, x+y, and z are values in the same range as in the above, and L and R are the same elements as those described above.
The present invention provides a piezoelectric element including the piezoelectric ceramic composition.